A lock-in amplifier of this type and a method of this type are known from the internship course material “Signalverarbeitung mit Lock-in-Verstärker” [“Signal processing with lock-in amplifier”] by the institute for solid state physics from the Technical University of Berlin. A modulated measurement signal, which contains signal components, in particular noise, is multiplied in a phase-sensitive detector (demodulator) with a reference signal for the modulation frequency and is therefore demodulated in a phase-sensitive manner. The demodulated measurement signal is subsequently integrated in an integrator (low-pass filter) over a predetermined integration duration (filter time constant) in order to extract the useful signal component of the measurement signal from the interference signal components.